I used to have a little fishing bobber just link photo below, that i got from WalMart.
Most of my fish were only interested in it for a second but i had one VT male who was a super aggro fish and the bobber got stuck under his filter outflow so it was constantly moving up and down in the water and the way the current was it was stuck in the one spot and didn't go anywhere else. This fish... i had to take it out of the water because I didn't want him to kill himself over it, he kept flaring at it and biting it and at the same time battling the filter current. I think he messed with it for about an hour before i took it out..
But he would attack anything that moved in his tank. I put my hand in once to push a plant back into the gravel that he pulled up and he bit me and didn't let go even after i pulled my hand out of the water, he hung on. Jerk of a fish i'm telling you. lol
I also have those floating Betta Logs and Marimo moss balls. My Bettas love playing with the Marimo, rubbing on it and when it floats at the surface they push it around.
A friend of mine likes to play with a laser light with her Bettas.